In a lighting device for a vehicle which uses a semiconductor light emitting device such as an LED (Light Emitting Diode) as the light source, a lighting control device for controlling an ON operation of the LED is mounted on the lighting device.
Some lighting control devices include a series regulator connected in series to an LED and controlling a specified current to flow to the LED, and a switching regulator for controlling an output voltage to be applied to the LED corresponding to a control state of the series regulator at a minimum voltage. Even if multiple LEDs are connected in series to, or in parallel with, the switching regulator, the switching regulator can control the output voltage to cause the specified current to flow to each of the LEDs.
In some cases in which an output of the switching regulator is short-circuited or grounded, however, a load of the switching regulator increases, causing a failure as the result of excessive power. In some cases in which the output of the switching regulator is opened as the result of a disconnection, the output voltage is excessively raised in a switching regulator of a flyback type, for example.
Therefore, it has been proposed to control a specified current to flow to a semiconductor light source (LED) through a series regulator, and to provide a switching regulator that controls an output voltage to be applied to the semiconductor light source (LED) at a minimum voltage depending on a control state of the series regulator. An operation of the switching regulator is stopped when an anode side of any semiconductor light source (LED) is grounded and an output side of the switching regulator is short-circuited, resulting in an abnormal drop in the output voltage (see, e.g., Japanese Patent Document JP-A-2006-103477).
An abnormality (if any) generated on the output side of the switching regulator is detected, thereby stopping the operation of the switching regulator to protect the LED. In the case in which each semiconductor light source (LED) is implemented as a multifunctional lamp, for example, a high beam, turn signal, cornering or DRL (Daytime Running Light) lamp, a burden on the power basis increases in the switching regulator. Even if multiple switching regulators are used, the burden on the power basis in one of the switching regulators increases.